1. Field of the Invention
The present invention relates chiefly to a piezoelectric quartz oscillator.
2. Description of the Prior Art
The use of oscillators with piezoelectric quartz resonators is becoming widespread for both consumer articles and professional equipment. Known types of oscillators have a piezoelectric resonator which is series-connected with an analog component of the linear amplifier type.
Prototypes of quartz oscillators using logic gates have been made. These oscillators have not been much developed because of their low performance.
The present invention enables the making of oscillators comprising piezoelectric resonators and at least one logic gate, these oscillators showing excellent performance characteristics and, especially, excellent short-term stability. Thus, an oscillator is obtained that has higher performance than an oscillator using analog circuits, with simplicity of construction and low cost derived from the use of the logic circuits.
The oscillator according to the present invention has a loop with the following elements connected in series: a logic gate, a piezoelectric resonator, phase-shifting means and voltage-increasing means. The output of the voltage-increasing means is connected to the input of the logic gate. Thus, the entire input dynamic range of the logic gate is used, and the load impedance of the piezoelectric resonator is reduced.
The short-term stability relates to short-term phase fluctuations of the signal coming from the oscillator. An ideal oscillator tuned to the resonance frequency f.sub.o, gives a Dirac peak at the frequency f.sub.o and no energy at other frequencies. Unfortunately, no such oscillator exists. In particular, an oscillator also generates energy around the frequency f.sub.o.
The oscillator according to the present invention enables a reduction in the short-term contribution of the energy generated around the frequency f.sub.o, at low cost and in an easily reproducible way.